Yeast Yeast 2008; 25: 537–548. Published online 10 July 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/yea.1603 Research Article Role of heterochromatin in suppressing subtelomeric recombination in fission yeast Kamlesh Kumar Bisht, Sumit Arora # , Shakil Ahmed ## and Jagmohan Singh* Institute of Microbial Technology, Sector 39A, Chandigarh-160039, India *Correspondence to: Jagmohan Singh, Institute of Microbial Technology, Sector 39A, Chandigarh-160039, India. E-mail: jag@imtech.res.in # Current address: Department of Pathology, Stanford University Medical Center, Stanford, CA 94305-5324, USA. ## Current address: Central Drug Research Institute, Lucknow (UP), India. Received: 20 March 2008 Accepted: 18 May 2008 Abstract Telomere length is regulated by a complex interplay of several factors, including telomerase, telomere-binding proteins, DNA replication machinery and recombina- tion. In yeast, DNA polymerase α is required for de novo synthesis of telomeres from broken ends of DNA, and it also suppresses the elongation of normal telomeric repeats. Heterochromatin proteins Clr1–Clr4 and Swi6 and DNA polα organize het- erochromatin structure at mating type, centromere, rDNA and telomere regions that are refractory to transcription and recombination in Schizosaccharomyces pombe. Here, we have addressed the role of heterochromatin structure in regulating the integrity and organization of telomeric regions. Here, we show that subtelomeric duplication and rearrangements occur in polα and heterochromatin mutants and find that some of the putative duplication events are dependent on the Rad50 path- way. Thus, our study shows a role of heterochromatin in maintaining the integrity of the subtelomeric regions by suppressing their recombination in Sz. pombe. Copyright  2008 John Wiley & Sons, Ltd. Keywords: Polα; heterochromatin; subtelomere; fission yeast; recombination Introduction Heterochromatin plays an important role in silenc- ing of mating type, centromere, rDNA and telom- ere regions in Schizosaccharomyces pombe (Elgin and Grewal, 2003; Klar, 2007). Maintenance of the structural integrity and function of telomeres is vital for cell viability and prevention of dis- ease in higher organisms. Because of the end- replication problem of DNA Polα, telomeres get shortened after every generation, which is com- pensated by elongation with telomerase (Savitsky et al., 2006). Absence of the trt1 + gene (encoding the catalytic subunit of telomerase) causes telomere shortening, which can be circumvented by chromo- somal circularization or telomeric recombination (Bhattacharyya and Lustig, 2006; Nakamura et al., 1998). Similar events occur in the rad3, tel1 dou- ble mutant (Naito et al., 1998). In ku70Δ strains, telomere shortening is compensated by the recom- bination of subtelomeric regions (Kibe et al., 2003; Shore, 2001). Heterochromatin may also play a role in telomere integrity in addition to silencing at mating type and centromeres; some heterochro- matin proteins, such as Taz1, Rap1, Swi6, Chp2 and Clr4, also play a role in silencing at telom- eres in Sz. pombe (Baur et al., 2001; Cooper et al., 1997; Nimmo et al., 1998; Thon and Klar, 1992). Interestingly, DNA Polα is also required for telom- ere silencing (Ahmed, 2001; Ahmed et al., 2001; Nakayama et al., 2001a). Recently, the SHREC complex, comprising Clr1–Clr2–Clr3, has been shown to be physically associated with the telom- ere to effect silencing (Sugiyama et al., 2007). Furthermore, deletion of Taz1, which binds to telomeric repeat sequences, can also elicit telomere fusions under meiosis and stress conditions through a Ku-dependent pathway (Ferreira and Cooper, 2001). Studies in the budding yeast have shown that heterochromatin regulates the telomere position effect, but surprisingly has no effect on telomere Copyright  2008 John Wiley & Sons, Ltd.